I'd say if you have something working don't upgrade just for the heck of it. But from recent personal experience I would highly recommend upgrading perl if you are doing development.

- newer perls let you be more free with perl grammar I find
- better (presumably, no anecdotes though) better error diagnosis in "perl -wc"
- When modules get updated sometimes they include code syntax or functions which are not available in old perls. -
- "perl -MCPAN -e shell" likes to try to build perl 5.8 for you when this happens
- but cpan is a lot easier to use than constantly building in other directories with stuff like "make pure_perl_install" etc. etc.
- and some modules just won't build so you have to go searching changelogs for the latest version which has what you want
- and possibly you are prey to bugs (I've seen some myself) in older perls, or even a buffer overflow (never seen one myself) in an old perl which was fixed at some time.
- presumably better performance and robustness (no concrete info for you sorry)
- Basically perl is as strong as its community and using an old perl is like giving yourself a lobotomy. A firewall doesn't maybe need so much in the brains department but if your brain grows you want to use the latest perl.

With one caveat - Cobalt RaQs which seem (RaQ3) to include vintage 1999 software use perl for their web admin interface. I have seen references on the net, some perosn even says it works fine with 5.6, but you shold realize that updating perl could break a current admin program which you must have (if you don't have root access).

Personally I now feel strongly that any product which embeds perl as part of its critical functionality should be using a separate perl installation which does not interfere with a user who wants to automatically update perl every 6 months or year without worrying about legacy code.